1. Field of the Invention
The present invention relates to a method and device for optically detecting the shape of the surface of a magnetic medium, the shape of the surface of a semiconductor wafer or the like. The invention relates more particularly to an inspection technique for detecting whether or not a data island that is arranged in the pattern formed on the surface of the medium and is finer than optical resolution is present or whether or not the shape of the data island is good, and detecting a foreign material or a scratch on the surface of the medium from the single illuminated region in a single process to detect whether or not the data island is present and whether or not the shape of the data island is good with high sensitivity and output or display the result of the detection.
2. Description of the Related Art
A medium composed of a (glass or aluminum) substrate and a magnetic material (deposited on the surface of the substrate) is used as a magnetic recording medium used in a magnetic hard disk storage device. The medium is magnetized by a magnetic head to ensure that data is magnetically recorded on the medium. The recording is performed on each of recording regions of the medium. Each of the recording regions corresponds to one bit that is a recording unit.
A medium used in a current recording format has a magnetic film formed on the entire surface thereof. A data region (corresponding to a recording region) and a servo region (in which a signal serving as a standard for a magnetic head is written) are written on the medium by a servo track writer. In order to increase a recording density of the medium, it is necessary to reduce an area of the data region per bit. When the recording area is reduced, however, an effect called heat fluctuation (causing reversal of a magnetic orientation due to heat) occurs. Thus, the increase in the recording density is limited.
In order to solve the above problem, the structure of the magnetic film, sensitivity of the magnetic head and the like has been improved. However, the increase in the recording density is limited. In recent years, a patterned medium has been expected as a recording medium to further increase the recording density. The patterned medium has thereon an array of magnetic structures each corresponding to one-bit recording information.
Two types of patterned media have been proposed until now: one is a discrete track medium shown in FIG. 2A; and the other is a bit patterned medium shown in FIG. 2B. The discrete track medium has a substrate 1000 and data islands (track pattern portions) 1001. The data islands 1001 are arranged in a concentric track pattern on the substrate 1000. A magnetic film is not present between the data islands 1001 arranged in the track pattern. This configuration reduces occurrence of a magnetic mutual interference between tracks of the medium. Thus, the discrete track medium has a reduced data region and an increased recording density compared with conventional media.
The bit patterned medium has a substrate 1000 and a large number of data islands (bit pattern portions) 1002. The data islands 1002 are formed by dividing data islands arranged in such a track pattern as shown in FIG. 2B in longitudinal direction of the data islands and are arranged in a pattern on the substrate 1000. Each of the data islands 1002 of the bit patterned medium stores one-bit data. Thus, the bit patterned medium has a further reduced data region and a significantly increased recording density compared with conventional media. The width of each of the data islands 1001 of the track pattern and the width of each of the data islands 1002 of the bit pattern are several ten nanometers. The two types of patterned media are known techniques.
A nano-imprint technique is a promising approach to form patterns in those media. FIGS. 3-1 to 3-6 show a process flow for forming a pattern using a nano-imprint technique.
(1) A mold 1003 is placed above a resist 1004 coated on the surface of a medium 1000. (2) The mold 1003 comes into contact with the resist 1004 and is pressed toward the resist 1004 to transform the resist 1004. (3) In this state, the resist 1004 is exposed to light coming from the side of the mold 1003. (4) The mold 1003 is removed, and the same pattern as that of the mold 1003 is formed in the resist 1004. (5) Portions of the medium 1000 on which the resist 1004 is not present are etched using a semiconductor lithography technique. (6) The resist 1004 is removed, and a bit pattern is formed in the medium 1000.
When the mold 1003 has a defect or a foreign material attached thereto, the transferred pattern may include a pattern failure or a fatal defect such as a lack of a data island. It is, therefore, necessary to inspect whether or not the bit pattern is appropriately formed.
Even when the bit pattern is normally formed using the nano-imprint technique, a foreign material attached after the nano-imprint process or a scratch generated after the nano-imprint process may impact the result of the inspection of the bit pattern. It is, therefore, necessary to determine whether or not a pattern failure is caused by a defect generated during the nano-imprint process or caused by a foreign material attached after the nano-imprint process or by a scratch generated after the nano-imprint process and to inspect the bit pattern with high sensitivity.
There is a scatterometry method in order to efficiently inspect a patterned medium formed by such a nano-imprint technique. JP-A-2007-133985 describes a technique for inspecting a patterned medium by means of the scatterometry method.